Let me state the obvious, its always better to get power at the source. Look into a DC compressor, a good one not a cheap one that will let you down when you need it most.
In the AC variety compressors, i do not think that you have a big enough inverter to run your porter cable, it looks like a 10 amp compressor and you barely have 8 amps. But for 99 bucks, you can get one of these; Blue Hawk .3 hp 2 gallon tank 125 PSI compressor that uses two amp, which is within your inverters capability. it will take 240 watts of your 1000 available to run it and it is a lot cheaper than a DC that will do the job.
http://www.lowes.com/pd_470440-30449-0120212A_0__
The problem I run into with my compressor is the regulator setting. You must set the lowest regulated pressure above the anticipated tire pressure, otherwise you will get into a no-mans land where your compressor is not getting a signal to operate because your tire and your compressor are in equilibrium. It creates a stalemate and your compressor will not activate. I ran into this problem and moved the regulator to 150 lbs max pressure and 125 min pressure. The max pressure for my trailer tires is 125 so I'm good.
The answer to your question is yes you can unplug the fridge and plug in your compressor, I least I would do it. But it will do no good, your inverter is good for about 8 amps if that much. The 1000 watt inverter, is that continuous or surge, if it has a peak of 1000 watts then that is bad because you have much less than 8 amps available, your porter cable is a 10 amp variety. meaning you need at least 1200 watts continuous to operate it.
The formula is volts X amp - watts
I have a residential refrig in my Landmark, so it has a 1000W inverter and two batteries. I have a Porter Cable 150 psi 120V pancake compressor that I use to ensure my tires are correctly inflated prior to leaving a campground. But if I needed to add air to a tire when not hooked up to shore power I assume that I can unplug the refig at the inverter and plug in the compressor to use it. Yes?
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